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Tracking Malaysia Air flight 370

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Story highlights

The search area for the plane covers sea and land, including 11 countries

The plane's pilots are a main investigation focus

Details have emerged about some key moments during the flight

As investigators search for clues to unravel the mystery of where Malaysia Airlines Flight 370 went, there were several key developments over the weekend.

But major questions still remain.

Here's a cheat sheet to help you get up to speed on the latest developments:

Where are investigators searching now?

The search has expanded to cover large swaths of land and sea, including 11 countries and deep oceans. Where the plane went is anybody's guess. As 26 nations help try to find the missing plane, there's also a process of elimination in which investigators try to piece together where the aircraft isn't. Pakistan said Sunday that the plane never showed up on its civilian radars and would have been treated as a threat if it had. The Times of India reported that India's military also said there was no way the plane could have flown over India without being picked up on radar.

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Malaysia's Prime Minister has said that somebody deliberately steered the plane off course. That means the pilots have become one obvious focus for investigators. On Sunday, Malaysian police said they were still investigating a flight simulator seized from pilot Zaharie Ahmad Shah's home. Peter Chong, a friend of the 53-year-old pilot's, said it's unfair to imply that Zaharie had anything to do with what happened to the plane. He said he'd been to Zaharie's house and tried out the flight simulator. "It's a reflection of his love for people," Chong said, "because he wants to share the joy of flying with his friends."

A 29-year-old Malaysian civil aviation engineer, Mohammed Khairul Amri Selamat, who works for a private jet charter company, was on the flight. Police are investigating all passengers and crew, but he is likely to be of particular interest because of his aviation knowledge. "I am confident that he is not involved," his father said. "They're welcome to investigate me and my family."

What do we know about key moments on the flight?

For days, we've been talking about the last transponder signal the plane sent. And now it appears another system that sends data about the plane, the Aircraft Communications Addressing and Reporting System, was shut off, too. Authorities say the last transmission from that system came early in the flight, at 1:07 a.m. But they say they don't know exactly when the system was shut down, as the next transmission wasn't due until 1:37 a.m. Someone inside the cockpit, believed to be the co-pilot, made the plane's last verbal communication with air traffic controllers at 1:19 a.m., saying, "All right, good night." The transponder was then switched off at 1:21 a.m., authorities say, and all civilian radar lost contact with the plane altogether about 1:30 a.m. Military radar last detected the plane at 2:15 a.m. off Malaysia's west coast, hundreds of miles off course. And at 8:11 a.m., more than seven hours after takeoff, a satellite made the last electronic connection, known as a "handshake," with the plane.

Though some details have come into focus, major questions remain unanswered:

Where's the plane?

Satellite and radar data have given authorities some clues but not enough to pinpoint the plane. Right now, investigators are focusing on two corridors where the plane might have either crashed or landed: a northern arc that stretches from the border of Kazakhstan and Turkmenistan in central Asia to northern Thailand, and a southern arc that spans from Indonesia to the southern Indian Ocean. Because the northern parts of the traffic corridor include some tightly guarded airspace over India, Pakistan and even some U.S. installations in Afghanistan, U.S. authorities believe it's more likely the aircraft crashed into waters outside of the reach of radar south of India, a U.S. official told CNN. If it had flown farther north, it's likely it would have been detected by radar. However, on Monday, an Indian military official told CNN that its military radar in the area of the Andaman and Nicobar Islands isn't as closely watched as it is in other areas. This leaves open the possibility that the flight may not have been picked up by Indian military radar around the time of its last believed Malaysian radar contact, near the island of Pulau Perak in the Strait of Malacca.

Who would deliberately divert it?

Photos:The search for MH370

Photos:The search for MH370

Two years after Malaysia Airlines Flight 370 went missing, a relative of one of the passengers burns incense in Beijing on March 8, 2016. Flight 370 vanished on March 8, 2014, as it flew from Kuala Lumpur, Malaysia, to Beijing. There were 239 people on board.

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Photos:The search for MH370

On July 29, police carry a piece of debris on Reunion Island, a French territory in the Indian Ocean. A week later, authorities confirmed that the debris was from the missing flight.

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Staff members with the Australian Transport Safety Bureau examine a piece of aircraft debris at their laboratory in Canberra, Australia, on July 20. The flap was found in June by residents on Pemba Island off the coast of Tanzania, and officials had said it was highly likely to have come from Flight 370. Experts at the Australian Transport Safety Bureau, which is heading up the search for the plane, confirmed that the part was indeed from the missing aircraft.

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Photos:The search for MH370

In late February, American tourist Blaine Gibson found a piece of plane debris off Mozambique, a discovery that renewed hope of solving the mystery of the missing flight. The piece measured 35 inches by 22 inches. A U.S. official said it was likely the wreckage came from a Boeing 777, which MH370 was.

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Relatives of the flight's passengers console each other outside the Malaysia Airlines office in Subang, Malaysia, on February 12, 2015. Protesters had demanded that the airline withdraw the statement that all 239 people aboard the plane were dead.

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A police officer watches a couple cry outside the airline's office building in Beijing after officials refused to meet with them on June 11, 2014. The couple's son was on the plane.

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Members of the media scramble to speak with Azharuddin Abdul Rahman, director general of Malaysia's Civil Aviation Department, at a hotel in Kuala Lumpur, Malaysia, on May 27, 2014. Data from communications between satellites and the missing flight was released the day before, more than two months after relatives of passengers said they requested it be made public.

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Operators aboard the Australian ship Ocean Shield move Bluefin-21, the U.S. Navy's autonomous underwater vehicle, into position to search for the jet on April 14, 2014.

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A member of the Royal New Zealand Air Force looks out of a window while searching for debris off the coast of western Australia on April 13, 2014.

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The HMS Echo, a vessel with the British Roya; Navy, moves through the waters of the southern Indian Ocean on April 12, 2014.

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A Royal Australian Air Force AP-3C Orion, on a mission to drop sonar buoys to assist in the search, flies past the Australian vessel Ocean Shield on April 9, 2014.

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A relative of a missing passenger cries at a vigil in Beijing on April 8, 2014.

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Australian Defense Force divers scan the water for debris in the southern Indian Ocean on April 7, 2014.

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A towed pinger locator is readied to be deployed off the deck of the Australian vessel Ocean Shield on April 7, 2014.

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A member of the Royal New Zealand Air Force looks at a flare in the Indian Ocean during search operations on April 4, 2014.

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On March 30, 2014, a woman in Kuala Lumpur prepares for an event in honor of those aboard Flight 370.

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The sole representative for the families of Flight 370 passengers leaves a conference at a Beijing hotel on March 28, 2014, after other relatives left en masse to protest the Malaysian government's response to their questions.

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A member of the Royal Australian Air Force is silhouetted against the southern Indian Ocean during the search for the missing jet on March 27, 2014.

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Flight Lt. Jayson Nichols looks at a map aboard a Royal Australian Air Force aircraft during a search on March 27, 2014.

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People in Kuala Lumpur light candles during a ceremony held for the missing flight's passengers on March 27, 2014.

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Malaysian Prime Minister Najib Razak, center, delivers a statement about the flight on March 24, 2014. Razak's announcement came after the airline sent a text message to relatives saying it "deeply regrets that we have to assume beyond any reasonable doubt that MH 370 has been lost and that none of those onboard survived."

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Grieving relatives of missing passengers leave a hotel in Beijing on March 24, 2014.

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A passenger views a weather map in the departures terminal of Kuala Lumpur International Airport on March 22, 2014.

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A Chinese satellite captured this image, released on March 22, 2014, of a floating object in the Indian Ocean, according to China's State Administration of Science. It was a possible lead in the search for the missing plane. Surveillance planes were looking for two objects spotted by satellite imagery in remote, treacherous waters more than 1,400 miles from the west coast of Australia.

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Photos:The search for MH370

Satellite imagery provided by the Australian Maritime Safety Authority on March 20, 2014, showed debris in the southern Indian Ocean that could have been from Flight 370. The announcement by Australian officials raised hopes of a breakthrough in the frustrating search.

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Another satellite shot provided by the Australian Maritime Safety Authority shows possible debris from the flight.

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A distraught relative of a missing passenger breaks down while talking to reporters at Kuala Lumpur International Airport on March 19, 2014.

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On March 18, 2014, a relative of a missing passenger tells reporters in Beijing about a hunger strike to protest authorities' handling of information about the missing jet.

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U.S. Navy crew members assist in search-and-rescue operations in the Indian Ocean on March 16, 2014.

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Members of the Chinese navy continue search operations on March 13, 2014. After starting in the sea between Malaysia and Vietnam, the plane's last confirmed location, search efforts expanded west into the Indian Ocean.

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A Vietnamese military official looks out an aircraft window during search operations March 13, 2014.

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Malaysian air force members look for debris near Kuala Lumpur on March 13, 2014.

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Relatives of missing passengers wait for the latest news at a hotel in Beijing on March 12, 2014.

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A member of the Vietnamese air force checks a map while searching for the missing plane on March 11, 2014.

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A Vietnamese air force plane found traces of oil that authorities had suspected to be from the missing Malaysia Airlines plane, the Vietnamese government online newspaper reported on March 8, 2014. However, a sample from the slick showed it was bunker oil, typically used to power large cargo ships, Malaysia's state news agency, Bernama, reported on March 10, 2014.

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A U.S. Navy Seahawk helicopter lands aboard the USS Pinckney to change crews on March 9, 2014, before returning to search for the missing plane in the Gulf of Thailand.

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Buddhist monks at Kuala Lumpur International Airport offer a special prayer for the missing passengers on March 9, 2014.

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Members of a Chinese emergency response team board a rescue vessel at the port of Sanya in China's Hainan province on March 9, 2014.

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The rescue vessel sets out from Sanya in the South China Sea on March 9, 2014.

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Malaysian Prime Minister Najib Razak, center, arrives to meet family members of missing passengers at the reception center at Kuala Lumpur International Airport on March 8, 2014.

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A relative of two missing passengers reacts at their home in Kuala Lumpur on March 8, 2014.

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In addition to the pilots, other passengers and crew members on board the plane, as well as any ground staff who came into contact with it, are under investigation. The bottom line, investigators say, is that whoever flew the plane off course for hours appeared to know what they were doing. Investigators are looking into the backgrounds of the passengers to see whether any of them were trained pilots. "There are still a few countries who have yet to respond to our request for a background check," said Khalid Abu Bakar, inspector general of the Royal Malaysian Police Force. "But there are a few ... foreign intelligence agencies who have cleared all the(ir) passengers."

Why would they do it, and how?

Finding a motive behind the plane's disappearance is a key problem investigators must solve. They haven't released any concrete details. Speculation has surged about the possibility of terrorism or hijacking, but that hasn't been confirmed.

Is there any chance the passengers and crew survived?

It's possible the plane's last satellite contact could have been made from the ground, as long as the airplane still had electrical power, Malaysia's civil aviation chief Azharuddin Abdul Rahman said Sunday. For the families and loved ones of those aboard Flight 370, some find comfort that there's no evidence the plane crashed. The father of one passenger, who watched updates from Malaysia in a Beijing hotel, said he hoped the plane was hijacked because that gave him reason to think his son had survived. "I hope they are alive," he said, "no matter how small the chance is."

Does the possibility that the plane is on land change anything about the investigation?

Yes, analysts said. It means it's even more pressing that authorities find the plane. "Time is even more of the essence. If this airplane has been taken to be used as a weapon, then the time that has been taken to prepare the aircraft for whatever deed is the plan -- obviously, to thwart that, it's all about time," said Shawn Pruchnicki, who teaches aviation safety and accident investigation at Ohio State University. CNN aviation analyst Jim Tilmon, a former American Airlines pilot, said that whoever deliberately steered the plane off course probably did it with help. But what's next is anyone's guess, he said. "We have been behind them all along," he said. "So now, if they had a plan, and if that plan included being able to set down someplace and refuel a little bit, we are looking at something that we may never see the end of."

Report: Plane flew low to avoid radar

Malaysian officials on Monday denied knowledge of a newspaper report that the plane may have dropped to an altitude of 5,000 feet to defeat commercial radar coverage. "We are not aware of that report, and that's a thing the investigative team has to look into. It does not come from us," Malaysia Airlines CEO Ahmad Jauhari Yahya told reporters in Kuala Lumpur. CNN could not immediately confirm the newspaper's account.

The report, published Monday by Malaysia's New Straits Times, said the flight dropped to 5,000 feet after turning back from its Kuala Lumpur-Beijing route on March 8 and quoted unnamed officials as saying "it's possible that the aircraft had hugged the terrain in some areas that are mountainous to avoid radar detection." New Straits Times Editor Farrah Naz Karim told CNN's "New Day" that the newspaper spoke to sources close to the investigation and asked how flying at that altitude could be done. She added that this is one aspect that investigators could be looking into but it's all speculation at this point.